Animation link: https://vlab.amrita.edu/repo/BIOTECH/BIC/Extraction_of_caffeine_from_tea/index.swf
Reagents Required:
- Dichloromethane.
- Anhydrous sodium sulfite.
- Distilled water.
Materials Required:
- Tea bags.
- Beaker (500ml).
- Hot plate.
- Separating funnel.
- Melting point apparatus.
Tea bags are used as the source of caffeine for this experiment.
Extraction step:
Sublimation step:
- Take 5 tea bags and record the weight of these tea bags.
- Take 500 ml beaker add 200 ml of distilled water to it. Now place the 5 tea bags in this beaker.
- Boil the contents in the beaker vigorously using a hot plate.
- Allow the mixture to cool for 5 minutes and then decant the mixture into another beaker.
- Gently squeeze the tea bags to liberate the rest of the water.
- Cool the aqueous solution to near room temperature.
- Continue cooling in an ice box, the tea must be cool (20° C) before coming in contact with dichloromethane (boiling point = 40° C).
- Extract the solution three times with 30-mL portions of dichloromethane (CH2Cl2). Do not get dichloromethane on your hands.
- a. The tea solution is poured into a separating funnel and 20ml of dichloromethane is added to it. The mixture will separate into two layers - the top layer is the tea layer and bottom layer is the dichloromethane since it is denser than tea.
b. Remove the funnel from the stand and keep your fingers on the stopper and carefully shake the separating funnel.
c. Vent the separating funnel periodically (every 30 sec) to relieve vapour pressure created inside the funnel.
d. When the contents have been sufficiently shaken place the separating funnel back on the ring stand and let the two layers separate.
e. Drain the bottom layer into a conical flask because now the caffeine is extracted into the dichloromethane layer. Cover the mouth of the conical flask to avoid evaporation of solution.
f. Repeat steps a) through e) twice.
- Dry the combined dichloromethane solutions with anhydrous Sodium sulfite. Add about 1 teaspoon of the drying agent until it no longer clumps together at the bottom of the flask. Mix well and leave it for 10 minutes.
- Decant the dichloromethane into a conical flask (100ml). Evaporate the dichloromethane solvent in a hot water bath.
- When all the solvent is removed you observe a residue of yellowish green - white crystalline caffeine.
- a.Take the conical flask containing crystalline caffeine.
b.Sublime the crude caffeine at atmospheric pressure by placing the flask directly on a pre-heated hot plate. Caffeine melts at 238°C and sublimes at 178°C.
c.Collect your sublimed caffeine by keeping a test tube on the mouth of the conical flask.
d.White vapour of caffeine sticking onto the test tube and the walls of the conical flask is observed.
e.Now cool the conical flask.
- Take a clean watch glass and record its weight in a weigh balance.
- Now strip off the caffeine from the conical flask and the walls of the test tube into the watch glass using a spatula.
- Record the weight of the watch glass + caffeine in a weigh balance and then find out the weight of extracted pure caffeine.
- The melting point of the extracted caffeine is determined using the melting point apparatus.
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